The present invention generally relates to material joining methods and apparatus and, in a preferred embodiment thereof, more particularly relates to sheet metal joining techniques used in the fabrication of air blower housings.
Centrifugal blowers of the type used, for example, to flow air through the cabinet of a forced air heating furnace are typically formed from an opposed pair of sheet metal scroll sides positioned against the curved opposite side edges of a sheet metal scroll wrap. A variety of techniques have been used to join the scroll wrap and sides to form the overall blower housing, including the use of spot welding, seam welding, screwing and crimping.
In an attempt to provide a less expensive method of joining the scroll sides to the scroll wrap, various proposals have been made to use tabs, formed on the scroll wrap side edges, as the joining structures. The tabs are inserted outwardly through corresponding slots spaced around the peripheries of the scroll sides, and then bent 90.degree. to interlock the scroll sides and wrap to form the blower housing. U.S. Pat. No. 4,787,818 to Bales et al is illustrative of this conventional tab-and-slot sheet metal joining technique being used in the fabrication of a centrifugal blower housing.
While this transverse bending of the scroll wrap tabs outwardly over the scroll side portions provides a relatively economical alternative to, for example, the use of spot or seam welding techniques, it has two primary disadvantages. First, due to material spring-back, the transversely bent tabs tend to form a relatively loose joint between the scroll sides and the scroll wrap, thereby undesirably permitting a certain degree of shifting between these joined portions of the blower housing. Second, the use of these tabs as joining elements does not lend itself to the automation of the overall joining process. The tabs typically have to be individually bent, thereby significantly lengthening the assembly time for the blower housing.
It can be seen from the foregoing that it would be desirable to provide improved tab look joining methods and apparatus for use in fabricating blower housings and in other joining applications involving adjacent deformable sheet members. It is accordingly an object of the present invention to provide such improved methods and apparatus.